Sucha device can be fixedin a waythatcircumvents foulingof the base
transducer (Kro»ger and Danielsson, 1997).
Opticalbiosensors
Opticalbiosensors, whichcan be classified into two groups, dependuponthe
specialproperties of light(see Fig. 19.4).In general theyofferadvantagessuch
as miniaturisationand disposability, and thereis no occurrenceof electrical
interference.Classical opticalbiosensors consist of fibreglass,whichhas been
coatedon one side with an enzymeor antibody. Directinformationwill be given
by suchtechniques as opticalwaveguide light-mode spectroscopy(OWLS)or
scanning anglereflectometry(SAR). In contrast to this the second group's
information is obtained at the expense of a completedescription of the adsorbed
layer (Ramsden, 1997); their most known examples are surface plasmon
resonance(SPR, see Fig. 19.5)and totalinternal reflexionfluorescence (TIRF)
or spectroscopy(TIRS).
Fig. 19.4 Overviewof opticalsensortechniques.Fig. 19.5 SPRprinciple:the samplewithanalyteis flowingoverthe surfaceof the
sensorchipwherethe bindingpartneris located.Interactionwiththeseimmobilised
moleculescan be monitoredby a changeof reflectedlight.Improvinghygieniccontrol by sensors 297